DE2842976A1 - ELECTROCHROME DEVICE - Google Patents

Description

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AMERICAN CYANAMIO COMPANY Wayne, New Jersey, V.St.A.

Electrochromic device

The invention relates to improvements in electro-optical Devices in which a layer of a persistent electrochromic material is in contact on an electrode is arranged with a special polymer electrolyte, which is also in contact with a counter electrode is in the device. In the operation of such devices, an electrical current is passed through the polymeric electrolyte conducted between the electrodes. Furthermore, the devices are provided with devices that make it possible to the Electrodes apply an electric field and reverse the polarity of the electrodes concerned so that the electric field Field is reversed in order to change the light absorption properties of the electrochromic layer.

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Ks are already known various devices of this type arise for numerous Änwendungsmöglichkeiten. For example, US Pat. No. 3,708,220 describes electrochromic devices of the type mentioned, in which a certain gel-like electrolyte solution is used.

U.S. Patent 3,521,941 discloses the possibility of using plastics such as polyesters, vinyl polymers or the like., of allyl polymers or the like. and of polycarbonates, Phenolic resins, amino resins, polyamides, polyimides and cellulosic resins in electrochromic devices. However no examples are given of the use of these polymers.

US Pat. No. 3,971,624 discloses the use of a perfluorinated sulfonic acid polymer as an electrolyte in electrochromic Devices are described, but no information is given as to how such a polymer becomes a component a device can be made.

Electrochromic devices become useful in digital displays and other display devices of images as well as in cases where the light transmittance is varied, e.g. in electrochromic Windows, mirrors and the like.

In a typical device of the present invention, a film is made of a particular persistent electrochromic material applied as a coating to a surface of an electron conductive electrode, which is usually a Plate is made of conductive glass, metal or carbon or the like. Is. Here, the layer forms from the electrochromic material on the electrode is the base on which the polymeric electrolyte is deposited so that the electrochromic layer comes into intimate contact with the polymer electrolyte in the device. On the top of precipitated polymer electrolyte becomes a counter-

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Electrode located different from the electrochromic Layer extending through the device. If an electric field is applied to the electrodes, an electric field flows Current through the polymer electrolyte between the electrochromic layer and the counter electrode, with either coloring or bleaching of the electrochromic material is brought about. Furthermore, with the devices Facilities are available which allow the polarity of the electrodes to be changed as required, in order to be used alternatively one polarity a coloring and with the opposite polarity a bleaching effect.

The invention is particularly directed to a method that enables a polymer electrolyte in electrochromic Bringing devices, the method in all of the aforementioned types of devices can apply. Furthermore, devices have been created by the invention in which improved electrolytes lead to faster switching and an extension of the service life, since damage to the electrolyte in occurs to a lesser extent. In order to introduce the polymeric electrolytes into the devices, the polymer is in dissolved in a suitable solvent, whereupon the polymer is deposited on the layer of the electrochromic material will; eventually the solvent is evaporated, so that a solid, hard film is formed from the polymeric electrolyte.

When trying to use electrochromic devices making stronger, self-supporting polymer films that are placed under pressure between electrodes contact problems at the interfaces between the solid electrolyte and the electrode. These contact problems can zu.führung that the device is partially or completely unusable. Also the use of liquid intermediate layers between the solid polymer and the elec-

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Troden leads to malfunctions due to the inevitable differences in the thickness of the liquid intermediate layers. In addition, the use of liquid interlayers contradicts the desire to use a solid polymer to to prevent dissolution or damage to the electrochromic layer as much as possible. When you look at polymers with elastomeric properties used to eliminate the initially occurring contact problems, a resolution develops or damage as the device ages and as the polymer is relieved from the applied pressure.

While it is theoretically possible to use a wide variety of polymers in such devices, it is experienced depending on the polymer selected, the important functions of the electrochromic devices vary considerably. To this Functions that are influenced here include, as the most important, the speed with which the electrochromic Layer switches from one state to another, furthermore the intensity of the coloration that occurs in the electrochromic layer is achieved, the electrical potential that is required for coloring the layer, as well as the electrical efficiency of the Shift operation.

The expression "switching ¹¹ here denotes the change in the polarity of the electrodes and the resulting change in the radiation absorption properties of the electrochromic material when an electric field is applied. The passage of a current in one direction through the device leads to an increase in the light absorption or the color of the Layer. If the current supply is interrupted, the layer tries to keep its absorption capacity unchanged, ie the color remains until a current of the opposite polarity is applied, whereupon the light absorption capacity of the layer is reduced at which the absorbency decreases is referred to as "fade ¹¹ ". The electrochromic material remains in each case

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its colored or bleached state after the supply of electricity has been interrupted.

The polymers which can be used as electrolytes according to the invention include soluble polymers and copolymers that contain acid or base groups. These groups are common covalently bound to the polymer chain.

The acidic types exchange cations while the basic types exchange anions. The main groups of cation exchangers in the strongly acidic type are -SO ₃ H and -PO ₃ H ₃ , while the weakly acidic type is -COOH. An example of the strongly basic type is -Cn ₀ N (CHo) ^ NOII, while an example of the weakly basic type is the group, NH ₀ OH. These four types contain sulfonic acid and

quaternary ammonium hydroxide highly ionized functions, and therefore they have a high conductivity for ions, which is due to the migration of H- or ÜH- ions. The properties of the ion group have a great influence on the ion conductivity of the ion exchange polymers. The polymers with the highest conductivity are those in which the mobile ion is a proton. The functional group -SO ₃ H is therefore preferable to its salts, for example -SO ₃ Na, or the weak acids such as -COOH. The extent of sulfonation also has an influence on the ionic conductivity of the polymer. Suitable polymers which are conductive for ions include, for example, polystyrene sulfonic acid, polyethylene sulfonic acid, perfluorosulfonic acid and any other polymers of the same general group.

Among the solvents that are suitable according to the invention for dissolving the polymers in order to produce the desired solution, include water and essentially all common organic solvents such as methanol, ethanol, acetone, methyl ethyl ketone, Methylene chloride, dimethylformamide, ethyl acetate and their homologous and analogous compounds. So it is possible to do any

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to use any solvent which is capable of dissolving the polymer and which can then be evaporated.

The electrolyte solutions can be easily prepared by adding a certain amount of the polymer to the Introduces solvent, whereupon the mixture is stirred with or without heating. The concentration of the polymer solution

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can vary between 10 mol / ltr and a saturated solution, but the actual concentration does not seem to be of decisive importance.

In order to introduce the polymer electrolyte into the electrochromic device, the polymer is on top of the electrochromic Layer applied with the help of a centrifugal process, by dipping, rolling or spraying. In the The production of small devices is preferably carried out using the centrifugal method, as this results in a more uniform, results in a more even layer of the polymer. When using this method to make a coating a polymer electrolyte is obtained which adheres firmly to the electrochromic film in the form of a coating, the The risk of creating harmful gaps or air spaces is at least largely eliminated.

The method according to the invention therefore includes measures for preparing a solution containing the polymer with a solvent which is suitable for the selected application method is suitable, as well as for applying a coating to the electrode surface. In general, the concentration is the Solution is not of crucial importance and can therefore vary within wide limits.

When using the spin process, the final thickness of the film is determined by the viscosity of the solution and the spin speed influenced. Solid polymer films 1 to 100 micrometers thick can be used

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achieve a solvent containing the polymer, if the viscosity of the solution is about 30 centistokes and the spin speed is about 500 to 5000 rpm.

When using the immersion method, the electrode is in dipped the polymer solution, pulled it out again, and then hung it to dry in a dust-free room. Thin Polymer films are formed when pulling out slowly, while thicker coatings are formed when the speed is increased Pulling out increased.

The polymer solution can also be applied to the electrode by rolling. In this procedure, the electrode passed between a set of rollers by means of which the polymer solution is applied to the electrode. A typical solution roll machine uses a drive roll to drive the electrode under the applicator roll to move through, which delivers the polymer solution to the electrode. A stripping roller is used to To regulate the amount of applied to the application roller polymer solution so that on the surface of the electrode exactly desired amount of the polymer is applied.

If a spraying process is used, it is necessary to to use a more dilute polymer solution compared to the methods described above. In this case a spray gun with a container can be used in conjunction with compressed air that is free of contaminants. When spraying of the coating, the electrode is held in a vertical position. To ensure full coverage, you can apply one or more coatings. Direct After the solution has been sprayed on, the electrode is brought into a horizontal position so that the coating has a flat surface may form while the solvent evaporates.

Embodiments of the invention are explained in more detail below.

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Example I.

An electrochromic device according to the invention was manufactured as follows:

Around an electrochromic window with variable light transmission a transparent, conductive glass coated with indium oxide was used as the starting material, as it is made by the Optical Coating Laboratory. This conductive glass substrate was made with a Coating in the form of a layer of electrochromic tungsten oxide. A thin protective layer was placed on top of this layer of WO “ applied from silicon oxide. A polystyrene sulfonic acid polymer, that from the National Starch Co. under the designation "Versa-TL = 500" was launched dialyzed and freed from impurities by freeze-drying. It became a solution of the polymer in methanol with a concentration of 70 mg / ml, which was used to deposit the layer of silicon oxide with the help of the To provide the centrifugal process with a coating. The substrate was arranged in a horizontal position on the centrifugal chuck, and the polymer solution was applied to the surface. The centrifuge was put into operation, and the speed was increased up to about 1000 rpm in order to throw off the excess polymer solution over the edges of the substrate so that a thin layer of the polymer remained, which was caused by evaporation of the solvent froze within a few seconds. After spinning, a second thin layer was applied to the polymer layer applied from silicon oxide. After that, a thin, see-through one Layer of palladium applied, followed by a layer of gold with a thickness of about 125 Å. To the A second glass plate was placed to seal the device, and the stands were sealed with an epoxy resin.

a second device has also been described in US Pat Manufactured, but the polystyrene sulfonic acid

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2 8 Λ 2 9 7 6

polymer used in the device in the form of a solid, thin film with a thickness of 75 microns.

Each of these devices could be discolored, discolored or erased when an electrical current was applied to a passed mean current density of about 1 µA / cm * '; at a permeability range of 50 to 20 *, vurdc with a Cycle of 15 seconds for dyeing, with a power interruption of 15 seconds, a time of 15 seconds for erasing and a power interruption worked from 15 see.

The following results were achieved:

Comparison device according to the invention contraption

It can be seen from this that applying the polymeric electrolyte in the manner described leads to a considerable improvement in the device.

Example II

The procedure of Example I was repeated, but the following polymer and solvent combinations were used, which were applied in the manner described. The devices thus made proved superior to those who did not use the method described for applying the electrolyte became.

A. Perfluorosulfonic acid in methanol B. polystyrene sulfonic acid in ethanol

C. Polyethylene sulfonic acid in water

D. Perfluorosulfonic acid in isopropanol

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Example III

An electrochromic device for displaying numerical information was produced, using as a starting material a transparent, conductive tin oxide glass was used. Tungsten oxide was deposited on the tin oxide, whereby a mask was used so that the precipitate was in the form of digits. The exposed tin oxide and the out Surfaces existing on tungsten oxide were coated with polymeric polystyrene sulfonic acid using the centrifugal method described was applied. Finally, a layer of palladium was applied to act as a counter electrode and more decorative Background for the electrochromic image came into effect. To color and see through the electrochromic digits to make, were in accordance with Example I. DC impulses fed.

Furthermore, a second display device has been described in US Pat Wise prepared, however, the polymeric polystyrene sulfonic acid was used used in the device in the form of a solid, thin film, which is essentially the same Strength was like the coating applied in the manner described.

Testing of the two devices according to Example I gave the following results:

Comparison device according to the invention

Work _{cycles 1800 Qic}

to failure

* Inoperable during the first working cycle due to uneven coloring.

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Claims (7)

EXPECTATIONS 1. Electrochromic device with a layer of one persistent electrochromic material that is on an electrode surface in electrical contact with a polymer electrolyte is arranged, a likewise in electrical contact with the polymer electrolyte counter-electrode and a electrical device suitable for applying electrical fields of opposite polarity to the electrodes, characterized in that the device has been provided with the polymeric electrolyte in that the polymer was dissolved in a solvent, so that the solution thus prepared was applied to the electrochromic material and that the solvent was removed from the applied coating by evaporation. 2. Device according to claim 1, characterized in that the electrochromic material is tungsten oxide (WO ₃ ). 3. Apparatus according to claim 1, characterized in that a method for applying the polymeric electrolyte was used, which was chosen from the group to which the centrifugal process, the dipping process, the roll-on process and the spraying process. 4. Apparatus according to claim 1, characterized in that the polymer electrolyte with the aid of the centrifugal process has been applied in the form of a coating. 5. Apparatus according to claim 1, characterized in that the polymer is a soluble polymer or copolymer, which contains acidic or basic groups. 909816/0752 6. Apparatus according to claim 5, characterized in that said groups are acidic groups. 7. Apparatus according to claim 6, characterized in that the acidic groups are -SO ₃ II groups S. Device according to claim 1, characterized in that the polymer is a polystyrene sulfonic acid polymer. 909816/0752